Selectively expanding spine cage with enhanced bone graft infusion

ABSTRACT

A selectively expanding spine cage has a minimized cross section in its unexpanded state that is smaller than the diameter of the neuroforamen through which it passes in the distracted spine. The cage conformably engages between the endplates of the adjacent vertebrae to effectively distract the anterior disc space, stabilize the motion segments and eliminate pathologic spine motion. Expanding selectively (anteriorly, along the vertical axis of the spine) rather than uniformly, the cage height increases and holds the vertebrae with fixation forces greater than adjacent bone and soft tissue failure forces in natural lordosis. Stability is thus achieved immediately, enabling patient function by eliminating painful motion. The cage shape intends to rest proximate to the anterior column cortices securing the desired spread and fixation, allowing for bone graft in, around, and through the implant for arthrodesis whereas for arthroplasty it fixes to endpoints but cushions the spine naturally.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/807,835 filed on Nov. 9, 2017, which is a continuation of U.S. patentapplication Ser. No. 14/689,634, filed on Apr. 17, 2015, which is acontinuation of U.S. patent application Ser. No. 13/799,047, filed onMar. 13, 2013, which is a continuation-in-part of U.S. patentapplication Ser. No. 13/183,080, filed on Jul. 14, 2011, which is acontinuation of U.S. patent application Ser. No. 11/535,432, filed onSep. 26, 2006, which claims priority from U.S. Provisional ApplicationNo. 60/720,784, filed on Sep. 26, 2005, the disclosures of which arehereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention generally relates to medical devices forstabilizing the vertebral motion segment. More particularly, the fieldof the invention relates to a remotely activated, hydraulicallycontrollable, selectively expanding cage (SEC) and method of insertionfor providing controlled spinal correction in three dimensions forimproved spinal intervertebral body distraction and fusion.

BACKGROUND

Conventional spine cages or implants are typically characterized by akidney bean-shaped body comprising a hydroxyapatite-coated surfaceprovided on the exterior surface for contact with adjacent vertebralsegments or endplates which are shown in FIG. 1 . A conventional spinecage is typically inserted in tandem posteriorly through theneuroforamen of the distracted spine after a trial implant creates apathway.

Such existing devices for interbody stabilization have important andsignificant limitations. These limitations include an inability toexpand and distract the endplates. Current devices for interbodystabilization include static spacers composed of titanium, PEEK, andhigh performance thermoplastic polymer produced by VICTREX, (Victrex USAInc, 3A Caledon Court, Greenville, S.C. 29615), carbon fiber, orresorbable polymers. Current interbody spacers do not maintain interbodylordosis and can contribute to the formation of a straight or evenkyphotic segment and the clinical problem of “flatback syndrome.”Separation of the endplates increases space available for the neuralelements, specifically the neural foramen. Existing static cages do notreliably improve space for the neural elements. Therefore, what isneeded is an expanding cage that will increase space for the neuralelements posteriorly between the vertebral bodies, or at least maintainthe natural bone contours to avoid neuropraxia (nerve stretch) orencroachment.

Another problem with conventional devices of interbody stabilizationincludes poor interface between bone and biomaterial. Conventionalstatic interbody spacers form a weak interface between bone andbiomaterial. Although the surface of such implants is typically providedwith a series of ridges or coated with hydroxyapetite, the ridges may bein parallel with applied horizontal vectors or side-to-side motion. Thatis, the ridges or coatings offer little resistance to movement appliedto either side of the endplates. Thus, nonunion is common in allograft,titanium and polymer spacers, due to motion between the implant and hostbone. Conventional devices typically do not expand between adjacentvertebrae.

Therefore, what is needed is a way to expand an implant to developimmediate fixation forces that can exceed the ultimate strength athealing. Such an expandable implant ideally will maximize stability ofthe interface and enhance stable fixation. The immediate fixation ofsuch an expandable interbody implant advantageously will providestability that is similar to that achieved at the time of healing. Suchan implant would have valuable implications in enhancing earlypost-operative rehabilitation for the patient.

Another problem of conventional interbody spacers is their largediameter requiring wide exposure. Existing devices used for interbodyspacers include structural allograft, threaded cages, cylindrical cages,and boomerang-shaped cages. Conventional devices have significantlimitation with regard to safety and efficacy. Regarding safety of theinterbody spacers, injury to neural elements may occur with placementfrom an anterior or posterior approach. A conventional spine cage lacksthe ability to expand, diminishing its fixation capabilities.

The risks to neural elements are primarily due to the disparity betweenthe large size of the cage required to adequately support the interbodyspace, and the small space available for insertion of the device,especially when placed from a posterior or transforaminal approach.Existing boomerang cages are shaped like a partially flattened kidneybean. Their implantation requires a wide exposure and potentialcompromise of vascular and neural structures, both because of theirinability to enter small and become larger, and due to the fact thattheir insertion requires mechanical manipulation during insertion andexpanding of the implant. Once current boomerang implants are preparedfor insertion via a trial spacer to make a pathway toward the anteriorspinal column, the existing static cage is shoved toward the end pointwith the hope that it will reach a desired anatomic destination. Giventhe proximity of nerve roots and vascular structures to the insertionsite, and the solid, relatively large size of conventional devices, suchconstraints predispose a patient to for aminal (nerve passage site)encroachment, and possible neural and vascular injury.

Therefore, what is needed is a minimally invasive expanding spine cagethat is capable of insertion with minimal invasion into a smalleraperture. Such a minimally invasive spine cage advantageously could beexpanded with completely positional control or adjustment in threedimensions by hydraulic force application through a connected thin,pliable hydraulic line. The thin hydraulic line would take the place ofrigid insertional tools, thereby completely preventing trauma todelicate nerve endings and nerve roots about the spinal column. Due tothe significant mechanical leverage developed by a hydraulic controlsystem, the same expanding cage could advantageously be inserted by aminimally-sized insertion guiding rod tool capable of directing the cagethrough the transforaminal approach to a predetermined destination, alsowith reduced risk of trauma to nerve roots. That is, the mechanicaladvantage is provided by a hydraulic control system controlled by thephysician external to the patient.

The minimally-sized insertion tool could house multiple hydraulic linesfor precise insertion and expansion of the cage, and simply detachedfrom the expanded cage after insertion. It is noted that in such ahydraulic system, a smaller, thinner line advantageously also increasesthe pounds per inch of adjusting force necessary to achieve properexpansion of the implant (as opposed to a manually powered ormanipulated surgical tool) that must apply force directly at theintervention site. That is, for a true minimally-invasive approach tospinal implant surgery what is needed is an apparatus and method forproviding the significant amount of force necessary to properly expandand adjust the cage against the vertebral endplates, safely away fromthe intervention site.

What is also needed is a smaller expanding spine cage that is easier tooperatively insert into a patient with minimal surgical trauma incontrast to conventional, relatively large devices that create theneedless trauma to nerve roots in the confined space of the vertebralregion.

Existing interbody implants have limited space available for bone graft.Adequate bone graft or bone graft substitute is critical for a solidinterbody arthrodesis. It would be desirable to provide an expandableinterbody cage that will permit a large volume of bone graft material tobe placed within the cage and around it, to fill the intervertebralspace. Additionally, conventional interbody implants lack the ability tostabilize endplates completely and prevent them from moving. Therefore,what is also needed is an expanding spine cage wherein the vertebral endplates are subject to forces that both distract them apart, and holdthem from moving. Such an interbody cage would be capable ofstabilization of the motion segment, thereby reducing micromotion, anddiscouraging the pseudoarthrosis (incomplete fusion) and pain.

Ideally, what is needed is a spine cage or implant that is capable ofincreasing its expansion in width anteriorly to open like a clam,spreading to a calculated degree. Furthermore, what is needed is a spinecage that can adjust the amount of not only overall anterior expansion,but also medial and lateral variable expansion so that both the normallordotic curve is maintained, and adjustments can be made for scoliosisor bone defects. Such a spine cage or implant would permit restorationof normal spinal alignment after surgery and hold the spine segmentstogether rigidly, mechanically, until healing occurs.

What is also needed is an expanding cage or implant that is capable ofholding the vertebral or joint sections with increased pullout strengthto minimize the chance of implant fixation loss during the period whenthe implant is becoming incorporated into the arthrodesis bone block.

It would also be desirable if such a cage could expand anteriorly awayfrom the neural structures and along the axis of the anterior spinalcolumn, rather than uniformly which would take up more space inside thevertebral body surfaces.

SUMMARY OF THE DISCLOSURE

In one implementation, the present disclosure is directed to aselectively expandable spinal implant for insertion between vertebrae ofa patient. The selectively expandable spinal implant comprises acylinder block defining at least first and second cylinders andcomprising a base configured for resting on a first vertebrae; at leastfirst and second pistons respectively received in the at least first andsecond cylinders, the pistons being extendable to impart a desiredspinal correction; and a bone engaging plate attached to the pistonsopposite the base for engaging a second vertebrae in response toextension of the pistons.

In another implementation, the present disclosure is directed to anapparatus for providing spinal correction. The apparatus includes animplant body configured and dimensioned for placement in anintervertebral space, the body defining a central cavity extendingthrough the body configured to receive bone graft material andcommunicate with the intervertebral space for infusion of the graftmaterial into the intervertebral space when placed therein, and a bonegraft supply passage extending through the body and communicating withthe central cavity; a bone graft material supply port disposed on theimplant body in communication with the bone graft supply passage, theport configured for attachment of a bone graft material supply line;first and second extendable members mounted on the body, one eachdisposed on an opposite side of the central cavity, the membersextendable from a first unexpanded height and to at least one expandedheight; and a plate with a bone engaging surface mounted on the firstand second extendable members, the plate defining an opening alignedwith the central cavity for passage there through of bone graft materialfrom the central cavity.

In yet another implementation, the present disclosure is directed to anapparatus for providing spinal correction. The apparatus includes animplant body configured and dimensioned for placement in anintervertebral space with a surface configured as a bone engagingsurface, the body configured as a cylinder block defining first andsecond cylinders opening opposite the bone engaging surface andcommunicating with at least one hydraulic fluid passage, a central, bonegraft material receiving cavity extending through the body, and a bonegraft supply passage communicating with the central cavity, wherein thecentral cavity is configured to open to intervertebral space forinfusion of the graft material into the intervertebral space when placedtherein; first and second extendable pistons sealingly received in thecylinders; a top plate with an opposed bone engaging surface mounted onthe first and second pistons, the top plate extendable with the pistonsfrom a first unexpanded implant height and to at least one expandedimplant height, the top plate defining an opening aligned with thecentral cavity for passage there through of bone graft material from thecentral cavity; a bone graft material supply port disposed on theimplant body in communication with the bone graft supply passage, theport configured for attachment of a bone graft material supply line; ahydraulic supply port disposed on the implant body adjacent the bonegraft material supply port, the hydraulic supply port communicating withthe at least one hydraulic fluid passage; and an attachment portdisposed on the implant body adjacent the supply port, the attachmentport being configured to receive and secure an implant insertion tool.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, the drawings show aspectsof one or more embodiments of the invention. However, it should beunderstood that the present invention is not limited to the precisearrangements and instrumentalities shown in the drawings, wherein:

FIG. 1 is a representation of the vertebral column showing posteriorinsertion and placement of the SEC between the number 4 and 5 lumbarvertebrae according to an aspect of the invention. Whereas this diagramshows the implant anteriorly in the vertebral interspace between lumbarbones 4 and 5, the majority of lumbar fusions are performed between L5and S1, into which implants are secured. The SEC can be used at anyspinal level the surgeon deems in need of fusion;

FIG. 2 is a side view of a vertebral body showing the placement of theSEC according to an aspect of the invention;

FIG. 3 is a top view of a vertebral body showing placement of the SECaccording to an aspect of the invention;

FIG. 4A is a front perspective view of the SEC in an unexpanded stateaccording to an aspect of the invention;

FIG. 4B is a rear perspective view of the SEC of FIG. 4A according to anaspect of the invention;

FIG. 4C is a rear perspective view of the SEC of FIG. 4A showing detailsof the hydraulic and bone graft input ports according to an aspect ofthe invention;

FIG. 4D is a perspective view of the SEC of FIG. 4A with the wedge plateremoved for clarity;

FIG. 4E is a perspective view of FIG. 4A showing the cylinders and bonegraft perfusing cavity defined by the SEC body according to an aspect ofthe invention;

FIG. 4F shows another view of the wedge plate according to an aspect ofthe invention;

FIG. 4G shows details of the wedge plate and lordosis plate according toan aspect of the invention;

FIG. 5A is a front perspective view of the SEC in an expanded stateaccording to an aspect of the invention;

FIG. 5B is a top perspective view of the SEC showing the cavity for bonegraft perfusion and recesses allowing lateral movement of the wedgeaccording to an aspect of the invention;

FIG. 5C is a rear perspective view of the SEC in an expanded stateaccording to an aspect of the invention;

FIG. 5D is a perspective view of FIG. 5C with the SEC body removed forclarity;

FIG. 6 is a perspective view of an alternative embodiment of the SECaccording to an aspect of the invention;

FIG. 7A is a perspective view of a master cylinder for hydraulic controlof the SEC according to an aspect of the invention. A variety ofalternative embodiments are available, most simply disposable syringesused for piston expansion;

FIG. 7B is a view of the interior of FIG. 7A;

FIG. 8 is a perspective view of an alternate embodiment of the mastercylinder according to an aspect of the invention;

FIG. 9A is a perspective view of the insertion tool holding the SEC,hydraulic lines and bone graft supply line according to an aspect of theinvention;

FIG. 9B is a close-up view of the insertion tool of FIG. 9A;

FIG. 10A shows one embodiment of a hydraulic line for independentcontrol of multiple slave cylinders according to an aspect of theinvention; and

FIG. 10B shows a close up of the fitting for the hydraulic line of FIG.10A according to an aspect of the invention.

FIG. 11 is a perspective view of a further alternative embodiment of anSEC according to another aspect of the invention.

FIG. 12 is a perspective distal view of the exemplary embodiment shownin FIG. 11 , with the top plate and pistons removed.

FIG. 13 shows a cross-section through line A-A in FIG. 11 .

FIG. 14 is a perspective view of the exemplary embodiment shown in FIG.11 with an attached insertion tool.

FIG. 15 is a perspective view of the exemplary embodiment shown in FIG.11 with an attached bone graft material supply line.

DETAILED DESCRIPTION

Referring to FIG. 1 , vertebral segments or end plates are shown with anaverage 8 mm gap representing an average intervertebral space. Acomplete discectomy is performed prior to the insertion of the SEC 100.The intervertebral disc occupying space 102 is removed using standardtechniques including rongeur, curettage, and endplate preparation tobleeding subcondral bone. The posterior longitudinal ligament is dividedto permit expansion of the intervertebral space.

The intervertebral space 102 is distracted to about 10 mm using arotating spatula (Not shown. This is a well-known device that looks likea wide screw driver that can be placed into the disc space horizontallyand turned 90 degrees to separate the endplates).

The SEC is inserted posteriorly (in the direction of arrow 102 betweenthe no. 4 and 5 lumbar vertebrae as shown in FIG. 1 (lateral view) orinto any selected intervertebral space. In accordance with an aspect ofthe invention, the SEC is reduced to small size in its unexpanded stateto enable it to be inserted posteriorly through space 102 as shown inFIG. 1 . In one exemplary embodiment, dimensions of an SEC are: 12 mmwide, 10 mm high and 28 mm long to facilitate posterior insertion andthereby minimize trauma to the patient and risk of injury to nerveroots. Once in place this exemplary SEC can expand to 16 mm, or 160percent of its unexpanded size, enabling 20 degrees or more of spinalcorrection medial and lateral. FIGS. 2 and 3 are a side view and topview, respectively, showing the placement of the SEC 100 on a vertebralbody.

FIG. 4A shows SEC 100 from the front or anterior position with respectto the vertebral column. The SEC is shown in a closed or unexpandedposition. Referring to FIGS. 4A through 4E, SEC 100 comprises a body orblock 106 that defines one or more slave cylinders 108 a, 108 b (bestseen in FIG. 5A) for corresponding pistons 110 a, 110 b. Pistons areprovided with O-rings 112 a, 112 b for a tight seal with the cylinder.The pistons and cylinders cooperate to provide hydraulically extendablemembers disposed within the body of SEC 100 in the unexpanded state.Block 106 also defines a central cavity 114 for infusion of bone graftmaterial into the intervertebral space when the SEC is fully expanded orduring the expansion process, as will be explained.

In general, bone graft material can be any substance that facilitatesbone growth and/or healing (whether naturally occurring or synthetic),such as, for example, osteoconduction (guiding the reparative growth ofthe natural bone), osteoinduction (encouraging undifferentiated cells tobecome active osteoblasts), and osteogenesis (living bone cells in thegraft material contribute to bone remodeling). Osteogenesis typicallyonly occurs with autografts.

As shown in FIG. 4C, block 106 further defines a central or main inputport 116 for attachment of hydraulic lines and a line for transmissionof a slurry or liquid bone graft material as will be explained. Theblock 106 defines a bone graft infusion conduit that extends from a bonegraft input port 119 located in main input port 116 to a bone graft exitport 120 (see FIG. 4D) located in central cavity 114 for infusion ofbone graft material therein.

Block 106 further defines local hydraulic fluid input ports 122 a, 122 b(FIG. 4C) that lead to corresponding slave cylinders 108 a, 108 b (FIG.5A) for driving the pistons and expanding the SEC by remote control froma master cylinder located ex vivo and with greatly increased force ascompared to conventional devices.

It will be appreciated that each slave piston 110 a, 110 b isindependently controlled by a separate hydraulic line 122 a, 122 bconnected to a master cylinder (as will be explained with reference toFIGS. 7 a through 8) located away from the patient and the site ofimplantation, thus minimizing active intervention by surgical tools inthe immediate vicinity of nerve roots. Although two slave cylinders areshown by way of example, it will be appreciated that the invention isnot so limited, but on the contrary, SEC block 106 easily is modifiableto define a multiplicity of slave cylinders, each controlledindependently by a separate hydraulic line, for expanding differentiallyto provide a substantially infinite variety of space-sensitiveadjustments for unique applications.

Referring again to FIGS. 4A through 4G, an anterior/posterior correctiveplate or wedge plate 124 is movably held in captured engagement on topof pistons 110 a, 110 b by corresponding hold down screws 126 a, and 126b. Plate 124 enables spinal correction in the anterior/posteriordirection as the cylinders expand vertically. Plate 124 has abone-engaging top surface provided with two elongated slots 128 a, 128 bin which the hold down screws sit. The elongated slots 128 a, 128 benable ease of expansion and facilitate angles between the pistons byallowing the plate 124 to move laterally slightly as pistonsdifferentially expand. The plate also defines cavity 114 for theinfusion of bone graft material, that is co-extensive with and the sameas cavity 114 defined by the SEC block. This enables perfusion of thebone graft material directly through the bone engaging surface of thewedge plate into the adjacent vertebral body.

Referring to FIGS. 4F and 4G, the anterior/posterior corrective plate124 is provided with a downwardly-extending edge 130 for engagement withthe pistons as they differentially expand, to ensure that wedge platestays firmly in place. Plate 124 provides anterior/posterior correctionin that it can be angled front to back like a wedge with a correctionangle a of 0-5 degrees or more. Plate 124 also defines bone graft cavity114 for enabling bone growth conductive or inductive agents tocommunicate directly with the engaged vertebral endplate.

The SEC is optionally provided with a lordosis base plate 132 thatincludes a bone engaging surface defining a cavity co-extensive withbone graft cavity 114 for enabling perfusion of bone graft material intothe adjacent engaged vertebral body. Lordosis base plate 132 also has ananterior/posterior angle b (refer to FIG. 4G) of 0-5 degrees forcorrecting lordosis.

Referring to FIG. 4G, top plate 124 and optional lordosis base plate 132function as two endplates providing a corrective surface that impactsvertebral bodies for spinal correction. Top plate 124 and lordosis baseplate 132 each include a bone-engaging surface 125 and 133,respectively, defining a cavity co-extensive with bone graft cavity 114for enabling perfusion of bone graft material into the adjacent opposedvertebral body. Lordosis base plate also has anterior/posterior angle bof 0-5 degrees for correcting lordosis. Thus, the wedge plate andlordosis base plate can provide lordotic correction of 10 degrees ormore.

Surgeon control over sagittal alignment is provided by differentialwedge shaping of the endplates and by calculated degrees of variablepiston expansion. The end plates will be constructed with 0 degrees ofwedge angle anterior to posterior, or 5 degrees. Therefore, the finalconstruct may have parallel end plates (two 0 degree endplates), 5degrees of lordosis (one 5 degree and one 0 degree endplate), or 10degrees of lordosis (two 5 degree implants). This implant permitsunprecedented flexibility in controlling spinal alignment in the coronaland sagittal planes.

Since vertebral end plates are held together at one end by a ligamentmuch like a clamshell, expansion of the pistons vertically against theend plates can be adjusted to create the desired anterior/posteriorcorrection angle. Thus, the top plate 124 does not need to be configuredas a wedge. Where an extreme anterior/posterior correction angle isdesired, the top plate and/or base plate may be angled as a wedge withthe corresponding correction angles set forth above.

FIGS. 5A through 5D show the SEC in its expanded state. Hydraulic fluidflows from a master cylinder (FIG. 7 A) into the cylinders throughseparate hydraulic input lines that attach to hydraulic input ports 122a, 122 b. Each hydraulic line is regulated independently therebyallowing a different quantity of material to fill each cylinder andpiston cavity pushing the pistons and medial/lateral wedge plate upwardto a desired height for effecting spinal correction.

In accordance with an aspect of the invention, the hydraulic fluidcommunicating the mechanical leverage from the master cylinder to theslave cylinder or syringe and pistons advantageously is atime-controlled curable polymer such as methyl methacrylate. Theviscosity and curing time can be adjusted by the formulation of anappropriate added catalyst as is well known. Such catalysts areavailable from LOCTITE Corp., 1001 Trout Brook Crossing, Rocky Hill,Conn. 06067. When the polymer cures, it hardens and locks the pistonsand thus the desired amount of spinal correction determined by thephysician is immovably in place.

It will be appreciated that the cylinder block 106 and pistons 110 a,110 b, comprise a biocompatible, substantially incompressible materialsuch as titanium, and preferably type 6-4 titanium alloy. Cylinder block106 and pistons 110 a, 110 b completely confine the curable polymer thatis acting as the hydraulic fluid for elevating the pistons. When thedesired spinal correction is achieved by the expanded pistons, thecurable polymer solidifies, locking the proper spinal alignmentsubstantially invariantly in place. The confinement of the polymer bythe titanium pistons and cylinder block provides the advantage of makingthe polymer and the desired amount of spinal alignment substantiallyimpervious to shear and compressive forces.

For example, even if it were possible to compress the polymer it couldonly be compressed to the structural limit of the confining cylinderblock. That is, by placing the curable polymer into the 6-4 titaniumcylinder block wherein two or more cylinders are expanded, the polymerbecomes essentially non-compressible especially in a lateral direction.It will be appreciated that 6-4 titanium cylinder block confining thehydraulic material provides extreme stability and resistance to lateralforces as compared to a conventional expanding implant. Further, thereis no deterioration of the curable polymer over time in term of itsstructural integrity because it is confined in the titanium alloy body.

The use of the present 6-4 titanium cylinder block configuration canwithstand compressive forces in excess of 12,000 Newtons orapproximately 3000 pounds of compressive force on the vertebrae. This isnot possible in a conventional expanding structure wherein the expandingpolymer is not confined by an essentially incompressible titanium body.

In accordance with another aspect of the invention, injectable bonegraft material 134 is provided along a separate bone graft input line tobone graft input port 119 for infusion into cavity 114 through bonegraft exit port 120.

The bone graft input line is controlled at the master cylinder or from aseparate source to enable a pressure-induced infusion of bone graftmaterial 134 through cavity of the bone engaging surfaces of the SECinto adjacent vertebral bone. Thus, the bone graft material fills, underpressure, the post-expansion space between adjacent vertebral bodies.This achieves substantially complete perfusion of osteo-inductive and/orosteo-conductive bone graft material in the post expansion space betweenthe vertebral bodies resulting in enhanced fusion (refer to FIGS. 5C,5D).

Referring to FIG. 6 , an alternate embodiment of the SEC comprisesmultiple slave cylinders and corresponding pistons 110 a, 110 b, 110 nare provided in SEC body 106. Each of the multiple slave cylinders andpistons 110 a, 110 b, 110 n is provided with a separate, associatedhydraulic line 122 a, 122 b, 122 n that communicates independently witha corresponding one of a plurality of cylinders in the master cylinderfor independently controlled expansion of the slave cylinders atmultiple elevations in three dimensions (X, Y and Z axes).

At the master cylinder, multiple threaded cylinders (or disposablesyringes) and pistons are provided, each communicating independentlythrough a separate hydraulic line 122 a, 122 b, 122 n with acorresponding one of the slave cylinders and pistons 110 a, 110 b, 110 nin the SEC.

The bone engaging surfaces of the multiple pistons 110 a, 110 b, 110 nprovide the corrective surface of the SEC. Thus, by appropriateadjustment of the pistons in the master cylinder, or depending on fluidinstalled via separate syringes, the surgeon can independently controlexpansion of the slave pistons in the SEC to achieve multiple elevationsin three dimensions for specialized corrective applications. A top orwedge plate is not necessary.

The bone engaging surface 111 of the slave pistons 110 a, 110 b, 110 nin the SEC may be provided with a specialized coating for bone ingrowthsuch as hydroxyapetite. Alternatively, the bone-engaging surface 111 ofthe SEC pistons may be corrugated, or otherwise provided with a seriesof bone engaging projections or cavities to enhance fusion.

As previously explained, the hydraulic fluid communicating themechanical leverage from the master cylinder to the SEC slave cylindersand pistons 110 a, 110 b, 110 n is a time-controlled curable polymersuch as methyl methacrylate that locks the SEC immovably in place aftercuring, at the desired three dimensional expansion.

As set forth above, injectable bone graft material is provided along aseparate bone graft input line to bone graft input port 119 for infusioninto cavity 114 and into the inter body space between the SEC andadjacent bone.

The surgeon by adjustment of the master cylinder is able to provideremotely a controlled angle of the SEC corrective surface to themedial/lateral (X axis) and in the anterior, posterior direction (Zaxis). The surgeon also can adjust the SEC in the vertical plane movingsuperiorly/inferiorly (Y axis) from the master cylinder or power/flowsource to control implant height. Thus, three-dimensional control isachieved remotely through a hydraulic line with minimal trauma to apatient. This aspect of the invention advantageously obviates the needto manually manipulate the SEC implant at the site of intervention toachieve desired angles of expansion. Such conventional manualmanipulation with surgical tools into the intervention site can requirefurther distracting of nerve roots and cause potential serious trauma toa patient.

Referring to FIGS. 7A and 7B, in accordance with an aspect of theinvention, a master cylinder 140 located remotely from the patient,provides controlled manipulation and adjustment of the SEC in threedimensions through independent hydraulic control of slave cylinders 110a, 110 b in the SEC. Master cylinder 140 comprises a cylinder block 142,defining two or more threaded cylinders 143. Corresponding screw downthreaded pistons are rotated downward into the threaded cylindersthereby applying force to a hydraulic fluid in corresponding hydrauliccontrol lines that communicate independently with and activatecorresponding slave cylinders 110 a, 110 b in the SEC with mechanicalleverage. The rotational force for applying the mechanical leverage atthe slave cylinders is controlled by thread pitch of the threadedpistons in the master cylinder, or in an alternate embodiment controlledby use of syringes, one acting as a master cylinder for each piston orslave cylinder to modulate piston elevation.

In FIG. 7B threaded pistons 144 a, 144 b are provided in hydrauliccylinders communicating through hydraulic lines 148 a, 148 b that arecoupled to hydraulic input ports 116 a, 116 b for independent hydrauliccontrol of slave cylinders 110 a, 110 b as previously explained.

Another threaded cylinder and piston assembly 150 is supplied with aquantity of bone graft material in slurry or liquid form and operates inthe same way to provide the bone graft material under pressure to theSEC bone graft input port 119 through bone graft supply line 152. Thus,bone graft material is forced under pressure from the master cylinderthrough cavity 114 and into the intervertebral space.

Referring to FIG. 8 , an alternate embodiment of a master cylinder isprovided for individual hydraulic control of each slave piston in theSEC implant. A master cylinder 154 is provided with two or morecylinders 156 a, 156 b, and associated pistons 157 a, 157 b. A lever 158controlled by the surgeon is attached to each piston. Hydraulic fluidfeeds through lines 148 a 148 b into the inserted SEC implant. The levercreates a ratio of 1 pound to 10 pounds of pressure inside the slavecylinders in the SEC and thus against vertebral end plates. Mechanicallythis provides a 10:1 advantage in lift force for the surgeon. Thesurgeon's required force application is multiplied via the lever andhydraulic system to create a controlled expansion of the SEC against theend plates as previously described to create any desired spine vertebralcorrectional effect in three dimensions.

If the surgeon uses one pound of force on the lever, the piston exerts10 pounds of force. The piston in the master cylinder displaces thehydraulic fluid through hydraulic lines 148 a, 148 b. The hydrauliclines are flexible conduit no more than 3 mm in diameter. Thin hydrauliclines are desirable to increase mechanical advantage at the slavecylinders in the SEC. If one pound of pressure is exerted on the handle,the corresponding piston in the SEC would have 10 pounds of liftingforce. If each slave piston inside the SEC implant has 200 pounds oflifting force, the required amount of pressure applied by the surgeon tothe master piston cylinder is 20 pounds, or one tenth the amount,consistent with the predetermined mechanical advantage.

In usual cases, where the surgeon has a patient in a partiallydistracted anatomic, anesthetized and relaxed position under anesthesia,30 pounds of force may be required for implant expansion upon thevertebral bone endplates. The surgeon in that case would need to applyonly 3 pounds of pressure to lever 158. Different ratios may beintroduced to optimize distraction force while minimizing injectionpressures.

The pressure application process is guided by normal surgicalprinciples, by visual checkpoints, and by a safety gauge thatillustrates the amount of expansion that has been exerted in directcorrelation with the implant expansion process. The gauge indicates theheight of the slave pistons and thus the vertical and angular expansionof the SEC. This translates to an ability to clarify the percentage oflateral expansion. That is, if the surgeon chooses to create an angle,he expands the right slave cylinder, for example, 14 mm and left slavecylinder 12 mm.

The master cylinder 154 preferably comprises transparent plastic toenable visual indication of the height of the hydraulic fluid therein,or a translucent plastic syringe to facilitate exact measured infusionof the slave cylinder implant expanding pistons. A knob 159 for settinggauge height is provided in each cylinder. An indicator attached to theknob registers the cylinder height with respect to a fill line, bleedline or maximum height line. The master cylinder and slave cylinders arefilled with hydraulic fluid. Air is removed by bleeding the cylinders ina well-known manner. The knob indicator is registered to the bleed line.A series of incremental marks are provided between the bleed line andthe maximum height line to show the surgeon the exact height of theslave cylinder in response to the surgeon's control inputs to the mastercylinder.

It will be appreciated that the master and slave hydraulic systeminteraction can have many equivalent variations. For example, the mastercylinder function of master cylinder 154 also can be provided by one ormore syringes. Each syringe acts as a master cylinder and is coupledindependently with a corresponding slave cylinder through a thinhydraulic line for independent activation as previously described. Asingle syringe acting as a master cylinder also may be selectivelycoupled with one or more slave cylinders for independent activation ofthe slave cylinders. As is well known, series of gradations are providedalong the length of the syringe that are calibrated to enable thesurgeon to effect a precise elevation of a selected piston at thecorresponding slave cylinder in the implant.

As previously explained, the SEC implant also expands vertically theintervertebral space from 10 mm to 16 mm or more. Additionally, bychanging the diameter of the piston inside the master cylinder, theforce exerted into the slave cylinder could be multiplied many fold soas to create major force differentials. The foregoing features providethe surgeon with an ability to establish a spinal correction system thatis a function of the needed change to correct a deformity, so as toproduce normal alignment.

Referring to FIG. 9A, it will be appreciated that hydraulic controllines 148 a and 148 b and bone graft supply line 152 are characterizedby a minimal size and are provided in the interior of a very narrowinsertion tool 180 (FIGS. 9A and 9B). The insertion tool 180 is smallenough to insert the SEC 100 posteriorly into the narrow insertionopening without risk of serious trauma to the patient. An enlarged viewof the insertion tool 180 (simplified for clarity) is shown in FIG. 9B.The insertion tool 180 includes a handle 182 and hollow interior forhousing hydraulic control lines and a bone graft supply line (not shownfor clarity). The hydraulic control lines and bone graft supply lineconnect through a proximal end of the insertion tool to the mastercylinder. A distal or insertion end of the tool holds the SEC 100. In apreferred mode, the insertion end of the insertion tool conformably fitsin the SEC hydraulic input port 116. Hydraulic control lines and thebone graft supply line are connected to the hydraulic input ports 122 a,122 b and bone graft supply input port respectively, prior to surgery.

The bone graft supply and hydraulic control lines are safely retractedafter the SEC is positioned. The hydraulic lines can be released bycutting after the operation since the hydraulic fluid hardens in place.

When the SEC is locked in position by the surgeon, the insertion tooland hydraulic tubes are removed and the curable polymer remains in theSEC slave cylinders.

In accordance with an aspect of the invention, the hydraulic fluidcontrolling the movement of the SEC is a time-controlled curable polymerthat hardens after a pre-determined time period, locking the SEC insertimmovably in a desired expanded position. The hydraulic fluid ispreferably methylmethacrylate or other similar inexpensive polymer, witha time-controlled curing rate. Time-controlled curable polymerstypically comprise a catalyst and a polymer. The catalyst can beformulated in a well-known manner to determine the time at which thepolymer solidifies. Such time-controlled curable polymers arecommercially available from several manufacturers such as LOCTITE Corp.,Henkel-Loctite, 1001 Trout Brook Crossing, Rocky Hill, Conn. 06067.

As is well understood by one skilled in the art, any equivalent curablepolymer that has a first flowable state for conveying hydraulic force,and that transitions to a second solid state upon curing may beemployed. In the first state, the curable polymer transfers theapplication of force hydraulically from the master cylinder to the slavecylinders, such that corrective action is achieved by elevating theslave pistons. The curable polymer transitions to a second solid stateupon curing such that the corrective elevation of the slave pistons islocked in place. Such an equivalent curable polymer is a polymer that iscured through the application of either visible or ultraviolet light orother radiation source which activates the polymer to transition to asolid state. Another methyl methacrylate liquid polymer when combinedwith powder becomes a viscous fluid as soon as the powder and liquid areblended; it is initially thin and free flowing. Gradually, in minutes,it begins to thicken, transforming state through paste and puddy tocement-like solid once inside the pistons, thus fixing the SEC at aprecise correction amount in its expanded position.

An example of such a light curable polymer is UV10LC-12 made by MASTERBOND Inc., of Hackensack, N.J. Such polymers are characterized by a fastcure time upon exposure to a visible or a UV light source. Dependingupon the intensity of the light source, cure times range from a fewseconds to less than a minute. As is well understood by one skilled inthe art, an extremely thin fiber optic line may be incorporated as anadditional line along with the multiple hydraulic lines shown in FIGS.10A and 10B for conveying light from a light source directly to thepolymer in the slave cylinders to effect curing.

Alternatively, a curable polymer may be activated by a radiation sourcesuch as low level electron beam radiation to cure or initiate curing. Anelectron beam advantageously can penetrate through material that isopaque to UV light and can be applied directly to lock the pistons intheir elevated or corrective position.

It will be appreciated that the amount of applied stress required tocause failure of the corrective implant is substantial due to theconfinement of the cured polymer completely within the body of theimplant, that is, the cylinder block that is comprised of 6-4 titanium.This is particularly advantageous since the confinement within thetitanium body enables the corrective position of the implant towithstand compressive forces up to the structural failure limit of thetitanium body; that is, to withstand compressive forces in a range offrom 8000 up to 12,000 Newtons.

Referring to FIGS. 10A and 10B, a hydraulic line 200 is provided forremote hydraulic control of a plurality of slave cylinders of the SECfrom a master cylinder. Hydraulic line 200 comprises a plurality ofindividual hydraulic lines 202 disposed about a central axis. Eachhydraulic line 202 provides independent activation of a separate slavecylinder from a master cylinder as previously explained. A bone graftsupply line 204 is provided along the central axis of line 200.Individual hydraulic lines 202 can be aligned and connected withcorresponding slave cylinder input ports prior to insertion of the SECfor providing independent hydraulic control to each of the slavecylinders. A threaded end 206 can be inserted into a similarly threadedcentral input port 116 of the SEC to prevent pull out.

In a further alternative embodiment of the present invention, asillustrated for example in FIGS. 11-15 , SEC 300 includes a block orbody 306 defining cylinders 308 for receiving pistons cooperating with atop plate 324 substantially as previously described. The body 306 of SEC300 also defines a central cavity 314 to receive bone graft material forcommunication with the intervertebral space when implanted. Top plate324 also provides a central opening aligned with central cavity 314 tofacilitate such communication. As shown, for example in FIG. 11 , topplate 324 may be provided with a textured bone engagement surface 311 onthe superior surface thereof and the central opening may be shaped tomatch the shape of central cavity 314. The textured surface isconfigured to provide for greater security and fixation between thevertebral body and SEC 300, and is not limited to the pattern shown, butmay be of any appropriate configuration for enhancing fixation as willbe appreciated by persons of ordinary skill in the art.

In this exemplary embodiment, SEC 300 includes a graft infusion port 319in communication with the central graft cavity 314, which may bepositioned laterally on a proximal face 386 of body 306 as shown in FIG.11 . Graft infusion port 319 may be located laterally of an attachmentport 383, which is where the insertion tool 380 is connected to the SEC300 via a threaded connector and rotary actuator 406 (see FIG. 14 ).Hydraulic line port 322, communicating with passages leading tocylinders 308, may be located laterally opposite attachment port 383 onproximal face 386 to receive hydraulic supply line 402 for actuation ofthe pistons. Distal face 396, opposite the attachment port, may presentnarrowed leading edge to facilitate insertion and placement of SEC 300between adjacent vertebral bodies.

As shown, for example, in FIGS. 12 and 13 , the graft infusion port 319communicates with the central cavity 314 through passage 392, whichtraverses the proximal wall 394 of block 306. Graft slurry or other bonegrowth promoting material infused through the graft port 319 flowsdirectly into the central cavity 314 from passage 392. The relativelylarge diameter of port 319 and passage 392 allow for unobstructed flowof material into the central cavity. Depending on the size of theimplant and the amount of height to be achieved through extension of thepistons, this can be particularly valuable because the central cavity314 enlarges as the SEC 300 expands. A free flow of bone graft materialwith sufficient volume is required to fill the enlarged volume ofcentral cavity 314 after expansion. For example, in an implant with awidth of about 18 mm, a length of about 50 mm, and a height of about 8mm, which is expanded after placement to a height of about 12 mm,passage 392 may have an internal diameter of about 6 mm. In general, toprovide an unobstructed flow of bone graft material, particularly inslurry form, passage 392 (and port 319) may be sized such that the ratioof the diameter of passage to the unexpanded implant height would be inthe range of about 55-80% or more specifically about 60-75%.

As previously mentioned, with the graft infusion port 319 locatedlateral of the attachment port 383, the bone graft supply line 404 ofinsertion tool 380 can also be located lateral to the hydraulic lines402 as shown in FIG. 14 . However, this parallel, lateral arrangementmay make insertion tool 380 wider, possibly creating difficulty inpassing sensitive neural structures in some anatomies. Where the lateralwidth of the insertion tool is of concern, such concern may be addressedby providing the bone graft supply line 404 separate from an insertiontool including only the rotary actuator 406 and hydraulic supply line402, such that bone graft supply line 404 may be placed separately andonly after the SEC 300 is implanted and expanded, and the insertion toolremoved, as shown in FIG. 15 . In this case, a collar may be providedthat also attaches in attachment port 319 to provide additional securityfor the bone graft supply line attachment.

In summary, remote hydraulic control of a spinal implant is particularlyadvantageous in a posterior insertion procedure because there is noanatomic room for mechanical linkage or tooling in the proximity of theadjacent spinal cord and neurovascular complex. The hydraulic controlprovided by the present invention provides significant mechanicalleverage and thus increased force to an extent that has not previouslybeen possible. Further, such hydraulic force is selective in bothdirection and magnitude of its application.

It is now possible to expand fenestrated endplates to support theanterior spinal column. This will create immediate and reliable firmfixation that will lead to immediate stabilization of the functionalspinal motion segment, and immediate correction of complex interbodydeformities in the sagittal and coronal plane.

The SEC provides advantages over currently existing technology thatinclude correction of coronal plane deformity; introduction of interbodylordosis and early stabilization of the interbody space with rigiditythat is greater than present spacer devices. This early stability mayimprove post-operative pain, preclude the need for posterior implantsincluding pedicle screws, and improve the rate of successfularthrodesis. Importantly, the SEC provides improvement of spaceavailable for the neural elements while improving lordosis. Traditionalimplants are limited to spacer effects, as passive fillers of theintervertebral disc locations awaiting eventual fusion if and when bonegraft in and around the implant fuses. By expanding and morphing intothe calculated shape which physiologically corrects spine angulation,the SEC immediately fixes the spine in its proper, painless, functionalposition. As infused osteoinductive/osteoconductive bone graft materialsheal, the patient becomes well and the implant becomes inert andquiescent, embedded in bone, and no longer needed.

While the invention has been described in connection with what arepresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not limited to thedisclosed exemplary embodiments and alternatives as set forth above, buton the contrary is intended to cover various modifications andequivalent arrangements included within the scope of the followingclaims.

For example, equivalent expansion surfaces can be provided forstabilizing the expanding SEC against the bone. Other compositions ofadditives may be used for the hydraulic fluid that achieves remotecontrolled expansion of the SEC in three dimensions. Similarly, varioustypes of biogenic fluid material for enhancing bone growth may beinjected through one or more lines to the SEC and different exitapertures may be provided to apply bone graft material to fill theintervertebral space, without departing from the scope of the invention.

The implant itself can be made of, for example, such materials astitanium, 64 titanium, or an alloy thereof, 316 or 321 stainless steel,biodegradeable and biologically active materials, e.g. stem cells, andpolymers, such as semi-crystalline, high purity polymers comprised ofrepeating monomers of two ether groups and a key tone group, e.g.polyaryetheretherketone (PEEK) TM, or teflon.

Finally, the implant may provide two or more pistons that are operatedconcurrently to provide coordinated medial/lateral adjustment of apatient's spine for scoliosis, with anterior/posterior adjustment of thepatient's spine to create natural lordosis, with relative anteriorexpansion greater than posterior expansion.

Therefore, persons of ordinary skill in this field are to understandthat all such equivalent processes, arrangements and modifications areto be included within the scope of the following claims.

Exemplary embodiments have been disclosed above and illustrated in theaccompanying drawings. It will be understood by those skilled in the artthat various changes, omissions and additions may be made to that whichis specifically disclosed herein without departing from the spirit andscope of the present invention.

The invention claimed is:
 1. A method for fusing first and secondvertebral bodies comprising: implanting an interbody implant between thefirst and second vertebral bodies using an insertion tool having asecond interlocking structure detachably interlocked with a firstinterlocking structure of a connector on the implant, so that a firstmember of the implant abuts the first vertebral body and a second memberof the implant abuts the second vertebral body, the implant having adistal portion positioned distally of a midpoint of the implant, and theinterbody implant having a proximal portion positioned proximally of themidpoint, wherein the implant has an aperture, the aperture and theconnector both being disposed on the proximal portion of the implant;expanding the implant having the aperture and the connector by movingthe first and second members away from each other, thereby increasingthe size of a cavity defined within the implant; and after the expandingstep, supplying a bone graft material into the cavity of the implantthrough the aperture such that the bone graft material moves from afirst location outside of the implant to a second location inside theimplant through the aperture.
 2. The method of claim 1, wherein theexpanding step comprises driving the first and second members away fromeach other by supplying a hydraulic fluid into the implant.
 3. Themethod of claim 2, wherein the hydraulic fluid is a curable polymer. 4.The method of claim 1, wherein the expanding step comprises extending aplurality of extendable members coupled to the first and second membersto move the first and second members away from each another.
 5. Themethod of claim 4, wherein the second member of the implant includes aplate mounted on the plurality of extendable members.
 6. The method ofclaim 4, wherein the expanding step comprises extending each of theplurality of extendable members independently of one another.
 7. Themethod of claim 4, wherein the cavity is defined within the implantbetween the plurality of extendable members.
 8. The method of claim 1,wherein the implanting step comprises a first surface of the firstmember of the implant abutting the first vertebral body and a secondsurface of the second member of the implant abutting the secondvertebral body, and wherein the supplying step comprises at least aportion of the bone graft material moving from a second location insideof the implant to a third location outside of the implant through anopening defined in each of the first and second surfaces of therespective first and second members.
 9. The method of claim 1, whereinthe supplying step comprises supplying the bone graft material into thecavity of the implant via the insertion tool.
 10. The method of claim 1,wherein the implant has a sidewall extending parallel to a direction ofexpansion when the first and second members move away from each otherduring the expanding step, and wherein the aperture and the connectorare laterally spaced apart from one another along the sidewall.
 11. Amethod for fusing first and second vertebral bodies comprising:implanting an interbody implant between the first and second vertebralbodies so that a first member of the implant abuts the first vertebralbody and a second member of the implant abuts the second vertebral body,the implant having an aperture; expanding the implant having theaperture from an unexpanded height to at least one expanded height bymoving the first and second members away from each other, therebyincreasing the size of a cavity defined within the implant; and afterthe expanding step, supplying a bone graft material into the cavity ofthe implant through the aperture such that the bone graft material movesfrom a first location outside of the implant to a second location insidethe implant through the aperture, wherein the aperture has a diameter inthe range of 55% to 80% of the unexpanded height of the implant.
 12. Themethod of claim 11, wherein the expanding step comprises driving thefirst and second members away from each other by supplying a hydraulicfluid into the implant.
 13. The method of claim 12, wherein thehydraulic fluid is a curable polymer.
 14. The method of claim 11,wherein the expanding step comprises extending a plurality of extendablemembers coupled to the first and second members to move the first andsecond members away from each another.
 15. The method of claim 14,wherein the second member of the implant includes a plate mounted on theplurality of extendable members.
 16. The method of claim 14, wherein theexpanding step comprises extending each of the plurality of extendablemembers independently of one another.
 17. The method of claim 14,wherein the cavity is defined within the implant between the pluralityof extendable members.
 18. The method of claim 11, wherein theimplanting step comprises a first surface of the first member of theimplant abutting the first vertebral body and a second surface of thesecond member of the implant abutting the second vertebral body, andwherein the supplying step comprises at least a portion of the bonegraft material moving from a second location inside of the implant to athird location outside of the implant through an opening defined in eachof the first and second surfaces of the respective first and secondmembers.
 19. The method of claim 11, wherein the supplying stepcomprises supplying the bone graft material into the cavity of theimplant via an insertion tool detachably coupled with the implant duringthe implanting step.
 20. The method of claim 11, wherein the implant hasa sidewall extending parallel to a direction of expansion when the firstand second members move away from each other during the expanding step,and wherein the aperture and the connector are laterally spaced apartfrom one another along the sidewall.